The present invention relates to a drum in a music box and more particularly to a drum which may have an external output shaft on which an attachment is to be fixed.
The music box can be divided broadly into two types. One is the type to enjoy the music playing and the other is the type to enjoy also the movement of the attachment such as dolls or the like in time to the music playing. The attachment is mounted to an external output shaft which rotates together with the drum.
In case the output is taken out from the drum shaft in accordance with the prior art, the external output shaft is formed in such a way as to be inserted into the central part of the drum and fixed thereto. Since the attachment is mounted to this external output shaft, an external force not only in the direction of rotation but also in the direction of axis is applied onto the shaft. Furthermore, it is required that the drum and the shaft be connected to each other by a sufficient force more than predetermined to be able to resist external forces.
The external output shaft is formed in such a way as to be inserted into the drum, thereby making it possible that the drum and the external output shaft are firmly connected to each other. However, it is required that they be connected to each other prior to the step of total assembly of the music box. It is important that the external output shaft be formed in such a way as to be inserted into the drum after the end of the step of total assembly.
There is a music box of a standard type which requires the external output shaft and a music box of a special type which does not require the external output shaft as mentioned herein. Thus, the external output shaft is not formed in such a way as to be inserted into the drum of every type.
Under such circumstances, drums of a standard type and special type are produced separately. In addition, in case the kinds of the programs of music to be played and of the external output shafts vary, the combination thereof results in various drums, thereby causing much management problems.
Furthermore, since the drum and bearing retaining mechanism are different between the standard type and the special type, it is required that the frame shape of the music box movement is prepared, taking into account the above mentioned difference. Then, there is further inconvenience in that the production and management problems increase.
In view of this defect, the present assignee has proposed a technique disclosed in the Japanese Utility Model Application Laid Open No. 1412/79, in which components such as a frame, a drum and the like are commonly used, and in which in particular, a bearing is separated into two members and thereafter, an external output shaft is assembled in the drum. However, since the bearing means for supporting the drum is fixed to the frame by press-fitting, the hollow bearing means will be deformed upon the press-fitting. Therefore, it is impossible in fact to assemble the output shaft in the drum after assembling the other parts. Also, the number of bearing members must be increased. This technique also will encounter the loss in production and management. The music box in which external output shafts are built is disadvantageous due to its physical size for transportation and packaging.